Synchronous data communications networks can carry payload data within a data stream using any one of a variety of physical layer communication protocols (e.g., using the Synchronous Digital Hierarchy (SDH), or Synchronous Optical Network (SONET) protocol). SONET and SDH use time-division multiplexing (TDM) to combine multiple “low-order” data blocks (such as a Tributary Unit (TU) in SDH, or a Virtual Tributary (VT) in SONET) into a “high-order” data block called a “frame” (e.g., an STS frame). The low-order blocks may be further sub-divided into segments of data associated with different channels.
It is sometimes useful to switch payload data from one channel to another channel using a cross-connect device. Channels can be switched in aggregate blocks. For example, a block of data in a location within a data stream corresponding to one VT time slot can be switched to a location within the data stream corresponding to another VT time slot. A cross-connect device that is capable of switching low-order blocks within high-order frames of a data stream can be built using a random access memory (RAM). An associated processor controls writing of an incoming data stream into the RAM and subsequent reading of an outgoing data stream from the RAM to provide cross-connection. The processor control logic and RAMs used to perform the switching are typically constructed in an integrated circuit.